1. Field of the Invention
This invention relates to improvements in the method of manufacturing a roll in which the shell portion of the body, the body core portion, and both shaft portions (right and left) of a large-sized roll for use in a rolling mill are integrally cast of different kinds of metal (alloyed metal) so as to be adapted for the different properties demanded from reasons of use and to a device preferably used for practising the method and more particularly to a device for disposing a lower side pouring sprue runner.
2. Prior Art
When the working outer shell (a surface of a roll body portion) of a roll, right and left shaft portions and a roll body core portion are different in required mechanical properties from each other, it was a practice to have recourse to such a centrifugal casting method as that in which molten metal for making the outer shell portion is cylindrically poured into a mold for a shell portion of a roll and hardened, thereafter the mold for a body portion of the roll is set upright, molds for shaft portions are assembled on the upper and lower ends of the body portion mold, molden metal is poured into the molds for the shaft portions and the body core portion to thereby integrally cast both the shaft and the body core portions.
In pouring molten metal for the shaft portions and the body core portion, the method described above makes it necessary not only to reduce as much as possible the time from after the centrifugal casting of the shell portion until removal of a body portion mold from a centrifugal casting machine, assembling the body portion mold with upper and lower shaft molds, and pouring molten core metal into the molds thus assembled, in order to prevent the temperature of outer shell metal from falling after it was hardened and to effect complete welding of the shell metal with the core metal poured, but also to consider that the high-temperature molten core metal may not cause any partial melting of the outer shell and may not produce non-uniformity in the thickness of the shell surface layer.
In pouring a molten core metal material, it was a practice to pour the material either through a lower pouring sprue runner connected beforehand integrally to a mold below the shaft portion or by an upper pouring method, and such a practice involves nothing troublesome so long as a roll to be cast is of such a small or a middle size as is at most about 900 mm or less in body diameter and about 2000 mm or less in body length. But when it comes to manufacturing such a large-sized roll as 1000 - 1250 mm in body diameter, 4500 - 5500 mm in body length, and 8000 - 9000 mm in overall length, it becomes necessary to use large molds, spend much time in assembling molds, and pour a large quantity of molten metal, and in addition there is a possibility that nonuniformity may be produced in the thickness of an outer shell and insufficiency may occur in the welding of the outer shell material to a core material.
Namely, it was always a problem that pouring the molten core material merely by a lower pouring method or an upper pouring method was too slow in casting speed. And further because the roll was long in body length, having recourse to one-way pouring method alone such as a lower pouring or an upper pouring method essentially increased the amount of the molten core material which passed in contact with either the lower or upper part alone of the outer shell portion, and in consequence the thickness of the outer shell wall either in the lower or in the upper area alone tended to be reduced in a greater degree than that in the other, thus there arising a problem which makes it difficult to obtain a uniform thickness of layer.
In addition thereto, the large-sized roll essentially resulted in an increase in the size of a mold for casting the roll, which fact, in turn, required much time in assembling the molds, which ultimately delayed starting to pour the molten core material. Especially, in the case where a lower pouring method is employed, the problem of damage given to a sprue runner by the vibrations resulting from asembling of molds was bottle-neck. Namely, the mold for the body portion of a large-sized roll is almost 2000 mm in outer diameter and 7000 mm in body length and as heavy as about 80 tons. After an outer shell was cast by centrifugal casting in such a large-sized body mold, the mold has to be removed from the centrifugal casting machine, set upright and assembled on the lower shaft portion mold beforehand mounted in the pit. But because the mold is large in size and heavy in weight, hasty assembling of molds provides eccentricity and wrong levelling of the molds, which in turn imparts heavy vibration to the lower mold to thereby damage the mold. And what makes matters worse, when a lower pouring sprue runner is connected to the lower mold, the overall length of a sprue runner amounts to as long as 9 to 10 m and vibration is transmitted to the sprue runner and damages the lining of the sprue runner and reduces the fixing of the sprue runner to the lower mold, with the result that attention on the part of workers to such a possibility would eventually demand scrupulous care and much time. Even when the sprue runner is connected to the lower mold after assembling of molds is over, crane operation involved in the connection would require unexpectedly much time in positioning the sprue runner without swinging and in fixing fastening pieces, stays, etc.